MYOLOGY 187 



poinds) and Short Extensor of the Thumb {Extensor primi 

 internodii pollicis) (Fig. 73, 14 ; Fig. 74, 19 ; Fig. 75, 20). — 

 United one to the other in man, blended in quadrupeds, 

 they form in the latter the muscles to which veterinary 

 anatomists give the name of oblique extensor of the meta- 

 carpus. 



This muscle arises from the median portion of the skeleton 

 of the forearm. There it is covered by the common extensor 

 of the digits and that of the small digit (anterior extensor 

 and lateral extensor of the phalanges). Then, at the in- 

 ternal border of the first of these muscles, it becomes super- 

 ficial, passes downwards and inwards, crosses superficially 

 the anterior extensor of the metacarpus, reaches the inferior 

 extremity of the radius, and becomes lodged in the most 

 internal of the grooves situated on the anterior surface 

 of this extremity, passes on the internal side of the carpus, 

 and is inserted into the superior extremity of the most 

 interna] metacarpal — that is, to the first metacarpal, or meta- 

 carpal of the thumb — in the dog and cat ; to the internal 

 rudimentary metacarpal in the horse. 



It is an extensor of the metacarpal into which it is in- 

 serted ; but as, if we recall the extreme examples given 

 above, in the dog the first metacarpal is not very mobile, 

 and in the horse the internal rudimentary metacarpal is 

 absolutely fixed to the bone which it accompanies, it is 

 more exact to add that this muscle is principally an extensor 

 of the metacarpus as a whole. 



And yet, in the cat and the dog, it is also able to adduct 

 the first metacarpal bone. It must be understood that this 

 movement would be abduction, if the hand could be placed 

 in the position of complete supination, as in the human 

 species. 



Long Extensor of the Thumb {Extensor secundi internodii 

 pollicis) a.nd Proper Extensor of the Index {Extensor indicts). 

 — These two muscles are blended together by their fleshy 

 bodies, so that the single name of proper extensor of the thumb 

 and index is preferable. This muscle is but of slight impor- 

 tance from our point of view, for it is extremely atrophied, 

 and so much the more as the number of the digits is lessened. 



